Vacuum heat insulator and apparatus using the same

ABSTRACT

A radiation heat transfer suppressor for inhibiting heat transfer by infrared rays is provided on the external surface of the enveloping member of a vacuum heat insulator. In heat-blocking or keep warm using a vacuum heat insulator, a surface having a radiation heat transfer suppressor is faced to a high-temperature side. Thus, the vacuum heat insulator exhibits excellent heat-insulating performance in a temperature range of 150° C. or higher.

This application is a U.S. National Phase Application of PCTInternational Application PCT/JP2004/009295.

TECHNICAL FIELD

The present invention relates to a vacuum heat insulator and apparatusesusing the vacuum heat insulator. It particularly relates to heatinsulation and keep warm in apparatuses having high-temperatureportions, including printing machines such as a copying machine andlaser printer, electronic equipment such as a computer, and further awater heater.

BACKGROUND ART

Energy saving has recently been desired because of the importance ofpreventing global warming, one of concerns over global environment. Inevery field, energy saving is promoted. Required for general equipmentusing heat or cold and members related to houses is a heat-insulatingmember having excellent heat-insulating performance in low- ormedium-temperature areas ranging from −30 to 150° C., from the viewpointof efficient use of heat. On the other hand, business equipment, such asa computer, printing machine, and copying machine, has a heating elementin its inside. To prevent the heat from conducting from the heatingelement to toners or internal precision components susceptible to heat,a high-performance heat-insulating member capable of being used attemperatures around 150° C. is strongly desired.

Among general heat-insulating members used in a temperature range around150° C., a vacuum heat insulator is used for applications requiring aheat-insulating member having higher performance. A vacuum heatinsulator is structured so that a core holding a space made by minutevoids is covered with an enveloping member for shielding entry ofambient air and the space is evacuated.

As the enveloping member of a vacuum heat insulator, a case of aheat-sealed metal can be used. In a low-temperature area requiring noheat resistance, a plastic-metal laminated film having a heat-seallayer, gas barrier layer, and protective layer, which is relativelyeasily bent and curbed, is often used as an enveloping member. Materialsof the core include powders, fibers, and open-cell foams.

In recent years, there have been wider-ranging demands for vacuum heatinsulators. Accordingly, vacuum heat insulators with much higherperformance are required. To improve heat insulation by blocking theimpact of radiation, a vacuum heat insulator using a calcium silicatemold including a radiant heat shield as a core is disclosed in JapanesePatent Unexamined Publication No. 10-160091. Also, to improve heatinsulation, a vacuum heat insulator that uses granulated composition towhich inorganic gel components and an infrared opaquer are added as acore is disclosed in Japanese Translation of PTC Publication No.2001-502367. Disclosed in Japanese Patent Unexamined Publication No.62-258293 is a technique in which a proper quantity of a synthetic resinfilm having a metal deposition surface formed thereon is mixed inpowdered heat insulator so that the synthetic resin film intersects andopposes the direction in which heat permeates.

However, the infrared ray, i.e. a factor of radiant heat, is absorbedwhen it reaches the enveloping member on the surface of a vacuum heatinsulator and, converted into heat energy to generate a state of solidheat conduction. For this reason, extremely little of the infrared rayreaches the core. Therefore, to improve heat insulation at temperaturesaround 150° C., suppression of transfer of radiant heat is necessary.The structures of these conventional techniques cannot address theseproblems sufficiently.

SUMMARY OF THE INVENTION

A vacuum heat insulator of the present invention includes a core, anenveloping member covering the core, and a radiation heat transfersuppressor disposed on the surface of the enveloping member on a hightemperature side thereof. The inside of the enveloping member isevacuated. This structure prevents infrared ray in the vacuum heatinsulator to be absorbed and suppresses radiation heat transferred tothe surface of the enveloping member. Thus, heat-insulating performanceis improved. The radiation heat transfer suppressor can be provided awayfrom the surface of the enveloping member.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view of a vacuum heat insulator in accordance withan exemplary embodiment of the present invention.

FIG. 2 is a sectional view of an essential part showing a fin of thevacuum heat insulator of FIG. 1.

FIG. 3 is an enlarged sectional view of a radiation heat transfersuppressor in the vacuum heat insulator of FIG. 1.

FIG. 4 is an enlarged sectional view of another radiation heat transfersuppressor in the vacuum heat insulator of FIG. 1.

FIG. 5 is a characteristics diagram showing a relation betweenwavelengths and black body emissivity at 150° C.

FIG. 6 is a characteristics diagram showing reflectance when light isperpendicularly incident on a silver-deposited surface.

FIGS. 7 to 9 are sectional views showing positional relations betweenthe vacuum heat insulator of FIG. 1 and heat generation source.

FIG. 10 is a schematic sectional view of an electric kettle inaccordance with the exemplary embodiment of the present invention.

FIG. 11 is a schematic sectional view of a notebook type computer inaccordance with the exemplary embodiment of the present invention.

FIG. 12 is a schematic sectional view of a projector in accordance withthe exemplary embodiment of the present invention.

FIG. 13 is a schematic sectional view of a printing machine inaccordance with the exemplary embodiment of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 is a sectional view of a vacuum heat insulator in accordance withan exemplary embodiment of the present invention. FIG. 2 is a sectionalview of an essential part showing a fin of the vacuum heat insulator.

In vacuum heat insulator 1, two sheets of enveloping member 3 facing toeach other cover core material 2. The inside of enveloping member 3 isevacuated almost to a vacuum and the periphery thereof is heat-sealed. Aglass wool mold is used for core 2.

Each sheet of enveloping member 3 has a laminated structure composed,from the inside, of heat seal layer 5, gas barrier layer 6, firstprotective layer 7, and second protective layer 8. For example,polychlorotrifluoroethylene (50-μm-thick) having a melting point of 210°C. is used for heat seal layer 5. For gas barrier layer 6, 6-μm-thickaluminum foil is used. For first protective layer 7,polyethylenenaphthalate (12-μm-thick) having a melting point of 270° C.is used. For second protective layer 8, tetrafluoroethylene-ethylenecopolymer (25-μm-thick) having a melting point of 260° C. is used.

As described above, heat seal layer 5 is made of a resin film having amelting point of 200° C. or higher. Melting points of gas-barrier layer6, protective layers 7 and 8 is higher than that of heat seal layer 5.Heat seal layer 5, gas barrier layer 6, and protective layers 7 and 8are flame-retardant films compliant with VTM-2 or higher of UL 94standard.

Heat insulator 1A is made of such core 2 and enveloping member 3. Infabrication of vacuum heat insulator body lA, two sheets of envelopingmember 3 are faced so that heat seal layers 5 are in contact with eachother, and three sides are heat-sealed to form a bag into which core 2is inserted. Sealing configurations of the bag include a four-sided sealtype, gusset bag type, three-sided seal type, pillow case type andcenter tape seal type. However, sealing configurations of the bag arenot limited to these. Core 2 is inserted into the bag of envelopingmember 3, its inside is evacuated to a pressure of 10 Pa, and theremaining one side is heat-sealed to fabricate vacuum heat insulatorbody 1A.

On the surface of enveloping member 3 on the high-temperature side whenvacuum heat insulator 1 is placed, radiation heat transfer suppressor 4is formed in various configurations. In other words, radiation heattransfer suppressor 4 is structured of a film for a coating includinginfrared reflection components and a film for suppressing radiation heattransfer. Further, this film is structured of either of alternatelylaminated inorganic films having different reflectances with each other,metal foil, and a resin substrate having a metal deposition film formedthereon. A description is provided of an example of radiation heattransfer suppressor 4 with reference to the accompanying drawings.

FIRST EXEMPLARY EMBODIMENT

First, a description is provided of a case in which a coating includingan infrared reflectance component is formed as radiation heat transfersuppressor 4. For samples 1 through 4, various kinds of coatings areformed on the surface of enveloping member 3 of vacuum heat insulatorbody 1A as radiation heat transfer suppressor 4. The heat-insulatingperformance of vacuum heat insulator 1 is evaluated by measuring thesurface temperature on the low-temperature side when a heat at 150° C.is applied to the surface on the high-temperature side.

Formed in sample 1 is a coating containing leafing aluminum flakepigment, i.e. a metal powder, as an infrared reflectance component andepoxy resin as a resin component. Formed in sample 2 is a coatingcontaining leafing aluminum flake pigment, similar to sample 1, andpolychlorotrifluoroethylene, i.e. a fluorocarbon resin, as a resincomponent. Formed in sample 3 is a coating containing silicon nitride,i.e. an inorganic powder, as an infrared reflectance component, andpolychlorotrifluoroethylene, i.e. a fluorocarbon resin, as a resincomponent. Formed in sample 4 is a coating containing titanium oxidepowder, i.e. a metal oxide powder, as an infrared reflectance component,and polychlorotrifluoroethylene. i.e. a fluorocarbon resin, as a resincomponent. Additionally, for comparison, vacuum heat insulator body 1Ahaving no coating is prepared. The measurement results are shown inTable 1.

TABLE 1 Infrared Surface reflectance temperature on compo-low-temperature Sample No. nent Resin component side 1 Leafing Epoxyresin 60° C. aluminum flake 2 Leafing Polychlorotrifluoroethylene 58° C.aluminum flake 3 Silicon Polychlorotrifluoroethylene 56° C. nitride 4Titanium Polychlorotrifluoroethylene 54° C. oxide Substrate None None80° C. 1A

As obvious from Table 1, the heat-insulating performance of samples Nos.1 through 4 has largely been improved in comparison with the case inwhich no coating is formed on vacuum heat insulator body 1A. In otherwords, the reflection of the infrared reflection components in coatingsformed on the surface of enveloping member 3 on the high-temperatureside prevents absorption of the infrared ray in vacuum heat insulator 1.Suppression of radiation heat transferred onto the surface of vacuumheat insulator 1 improves heat-insulating performance. The coating caneasily be provided uniformly on radiation heat transfer suppressor 4even when the surface of body 1A is non-flat or non-uniform. This canprovide excellent productivity and exert effects of suppressingradiation heat transfer.

The metal powder used for a coating of radiation heat transfersuppressor 4 has a low emissivity and excellent effects in infraredreflection capability. This effectively suppresses radiation heattransferred to the surface of vacuum heat insulator 1, thus improvingheat-insulating performance. As a metal powder, any materials havingfunctions of direct reflection and distribution of infrared rays can beused. Among those, at the view point of improving heat-insulatingeffects, it is desirable that the reflectance especially in a wavelengthranging from 2 to 25 μm is at least 20%, more preferably at least 50%.Materials having smaller emissivity, such as flake aluminum powder,similar silver powder and copper powder, are desirable because they havelarger infrared reflection effects.

Additionally, it is preferable that the thickness of the coating rangesfrom 1 to 100 μm. More preferably, it ranges from 10 to 50 μm. With athickness less than 1 μm, the effect is insufficient; with a thicknessover 100 μm, the coating may peel off. In formation of the coating, aprimer layer and overlay can be formed in some applications of vacuumheat insulator 1.

The surface temperature on the lower-temperature side of sample 2 is 2°C. lower than that of sample 1. This is thought because, in the use of afluorocarbon resin having a relatively smaller range of absorptionwavelengths in an infrared range from 2 to 5 μm as a resin component,absorption of heat rays by resin components in the coating suppresses anincrease in solid heat conduction. Because the melting point of thefluorocarbon resin is 200° C. or higher, resin components do not melteven at high temperatures of approx. 150° C. For this reason, excellenteffects of suppressing radiation heat transfer are exerted for anextended period of time. In other words, it is preferable that thecoating has a resin component of 200° C. or higher. When ambienttemperature at which vacuum heat insulator 1 is used is set to 50K lowerthan the melting point of the resin component, a resin component havinga melting point of 200° C. or higher does not melt out even at hightemperatures of approx. 150° C. This structure can exert excellenteffects of suppressing radiation heat and provide excellentheat-insulating performance.

Fluorocarbon resins having a relatively small range of infraredabsorption wavelength can be used. Such fluorocarbon resins includepolychlorotrifluoroethylene, tetrafluoroethylene-ethylene copolymer, andtetrafluoroethylene-hexafluoropolypropylene copolymer. Thesefluorocarbon resins have melting points of 200° C. or higher.

In sample 3, the temperature on the low-temperature side of sample 3 is2° C. lower than that of sample 2. Because inorganic powders alsoreflect infrared rays, the radiation heat transferred onto the surfaceof vacuum heat insulator 1 is effectively suppressed, and thus theheat-insulating performance is improved. Also, because the solid heatconductivity of silicon nitride, i.e. the inorganic powder, is lowerthan those of metals, an increase in the solid heat conductivity issuppressed.

As inorganic powders used for the coating, those known can be used ifthey have an infrared ray reflection function. Various kinds ofinorganic particles, such as glass bead, nitrides such as boron nitrideand titanium nitride, hydroxides such as iron hydroxide, aluminumhydroxide, and magnesium hydroxide, and sulfides such as cupper sulfideand zinc sulfide, can be used. Among these inorganic particles, thosehaving low solid heat conductivities are preferable.

In sample 4, the surface temperature on the low-temperature side is 2°C. lower than that of sample 4. This is because the effect of scatteringis added to the relatively small solid heat conductivity of titaniumoxide powder, i.e. a metal oxide powder as the infrared ray reflectioncomponent. In other words, because metal oxides have effects ofscattering and reflecting infrared rays, the radiation heat transferredonto the surface of vacuum heat insulator 1 is effectively suppressedand heat-insulating performance is improved.

As metal oxide powders used for the coating, any materials capable ofreflecting and scattering infrared rays can be used. Iron oxide, tinoxide, zirconium oxide, titanium oxide, manganese oxide, bariumtitanate, ferric chromate, antimony-doped tin oxide, tin-doped indiumoxide, and the like can be used. Among metal oxide powders, those havinglow solid heat conductivities are preferable.

Any known coating composition may be included in the coating if itcontains infrared reflection components. In some applications, two ormore kinds of metal powders, inorganic powders, and metal oxide powderscan be mixed properly.

SECOND EXEMPLARY EMBODIMENT

Next, a description is provided of radiation heat transfer suppressor 4formed of a laminate of inorganic material films having differentreflectances. The basic structure of the vacuum heat insulator issimilar to those of FIGS. 1 and 2 in accordance with the first exemplaryembodiment.

FIG. 3 is a sectional view of radiation heat transfer suppressor 4 inaccordance with this embodiment. Radiation heat conduction suppressor 4of this embodiment is a radiation heat suppressing film in which firstinorganic film 11 made of magnesium fluoride and second inorganic film12 made of calcium fluoride and having a different reflectance arealternately laminated in four layers.

When inorganic material films having different reflectances arealternately laminated in a thickness of the quarter of a specificwavelength, fronts of the waves reflected from the boundary surfaces ofrespective layers overlap additively. This allows the wavelength of farinfrared rays to selectively reflect. Now, the specific wavelength showsa wavelength in the vicinity of providing maximum emissivity at aheat-insulating temperature. The specific wavelength varies withapplicable temperatures. At 150° C., for example, the specificwavelength ranges from 4 μm to 10 μm. Setting the specific wavelengtheffectively can prevent absorption of infrared rays, effectivelysuppress radiation heat transferred to the surface of vacuum heatinsulator 1, and improve its heat-insulating performance.

Vacuum heat insulator 1 structured as above reflects most of theinfrared rays generated from the heat source at radiation heat transfersuppressor 4 provided on the surface of vacuum heat insulator 1. Thisreflection prevents infrared rays from being absorbed by protectivelayer 9 of enveloping member 6, thus generating no heat leak. As aresult, the heat conductivity caused by radiation transfer is reducedand the heat conductivity of vacuum heat insulator 1 is reduced.

In this embodiment, a radiation heat suppressing film is structured byalternately laminating magnesium fluoride and calcium fluoride. To makemaximum use of reflection on the boundary surfaces, a film havinganother reflectance can be laminated, and the materials of the film isnot specifically limited. The materials include magnesium fluoride,calcium fluoride, lithium fluoride, barium fluoride, thalliumbromo-iodide, thallium bromo-chloride, sodium chloride, potassiumbromide, potassium chloride, silicon oxide, cesium iodide, zincselenide, and the like.

The thickness of the film is not specified. However, a smaller thicknessreduces shock resistance; a larger thickness increases the solid heatconductivity as a vacuum heat insulator. For this reason, in formationof a radiation heat suppressing film by deposition, such as physicalvapor deposition (PVD) method and chemical vapor deposition (CVD)method, it is preferable that the thickness of the film ranges from 5 nmto 10 μm.

Considered methods of forming the radiation heat suppressing filminclude sputtering, deposition, PVD method, CVD method, or electrodeposition methods on enveloping member, or bonding a film thereon by anadhesive. However, the method of forming a film is not specified. Thefilm may be laminated together with a thin layer made of inorganicmaterials or semiconductors.

In addition to an inorganic material film laminate, a fluorocarbon resinfilm can be laminated. Fluorocarbon resins absorb a smaller number ofwavelengths in the wavelength range of infrared rays (2 to 25 μm), i.e.heat rays, and do not absorb infrared rays. As a result, infrared raysare transferred to the inorganic material film laminate, similar to thecase of the first exemplary embodiment. The inorganic material filmlaminate reflects the infrared rays. This reflection suppressesabsorption of infrared rays on the surface of vacuum heat insulator bodylA, thus improving heat-insulating performance. Additionally, providinga fluorocarbon resin on the outermost layer of radiation heat transfersuppressor 4 increases the durability of heat radiation conductionsuppressor 4. This mechanism also applies to the third exemplaryembodiment, which will be described below.

THIRD EXEMPLARY EMBODIMENT

Next, a description is provided of a case in which radiation heattransfer suppressor 4 is formed of a metal film. The basic structure ofthe vacuum heat insulator is similar to those of FIGS. 1 and 2 inaccordance with the first exemplary embodiment.

In this embodiment, a metal film forming radiation heat transfersuppressor 4 is made of a metal foil or laminating them. Alternatively,as shown in the sectional view of FIG. 4, the metal film can be made ofa thin layer of metal film 13 formed by deposition, sputtering, orelectrode position method, or a laminate thereof. The metal film canalso be made by laminating a metal film with thin layers of inorganicmaterials or semiconductors.

FIG. 5 is a characteristics diagram showing a relation between blackbody emissivity and wavelengths at 150° C. FIG. 6 is a characteristicsdiagram showing reflectance when light is perpendicularly incident on asilver (Ag)-deposited surface.

When a heat at 150° C. is applied to the surface of vacuum heatinsulator 1 on the high-temperature side, the relation betweenwavelength λ and radiation emissivity Ebλ follows the Planck low, thewavelengths generated from the heat source of 150° C. are concentratedon the far infrared area as shown in FIG. 5. Under this assumption, thereflectance when light is perpendicularly incident to the Ag-depositedsurface is shown in FIG. 6, the reflectance in the far infrared area areextremely high at 99%. On the other hand, in vacuum heat insulator body1A having no radiation heat transfer suppressor 4, protective layers 7and 8 absorb far infrared rays to generate heat. For this reason, thereis a large difference in heat-insulating performance. In this manner,metal films have high reflectances, thus effectively reflecting infraredrays. This reflection effectively prevents absorbs of infrared rays invacuum heat insulator body 1A and inhibits radiation heat transferred onthe surface of vacuum heat insulator body 1A. These effects improveheat-insulating performance.

In the above description, Ag is used as the metal. However, any kind andthickness of materials having an infrared ray reflection function, suchas gold (Au), aluminum (Al), and cupper (Cu), can be used. When thereflectance in a wavelength area ranging from 2 to 25 μm is 20% orlarger, the heat-insulating performance improves. Preferably, at areflectance of 50% or larger, a synergistic effect with vacuum heatinsulator body 1A can provide a larger heat-insulating performance.

The thickness of the film is not specified. A smaller thickness reducesshock resistance; a larger thickness increases the solid heatconductivity as a vacuum heat insulator. Thus, preferably, the thicknessof the film ranges from 5 nm to 10 μm when the film is formed by a gasphase method, such as deposition. Preferably, the thickness of the filmranges from 1 μm to 30 μm when the film is formed by laminating metalfoils. Preferably, the thickness of the metal foil ranges from 1 μm to100 μm, and more preferably, from 10 μm to 50 μm. At a foil thicknesssmaller than 1 μm, insufficient strength causes difficulty in handling.At a thickness of 100 μm or larger, infrared ray reflection effectsreach saturation. At a thickness of 100 μm or larger, the solid heatconductivity may increase when the film is placed in contact with vacuumheat insulator body 1A.

Considered as a method of forming metal film 13 is sputtering ordeposition on enveloping member 3, or bonding a film by an adhesive.However, the method of forming a film is not specified.

When oxidization of the surface or weather resistance of the metal filmcauses some troubles, a layer made of a fluorocarbon resin can be formedon the surface of the metal film. Specific examples are given below.

First, metal foils are placed as radiation heat transfer suppressor 4.The results obtained by changing the kinds of metal foils are shown insamples 5 to 7.

Used as core 2 in these samples are uniformly mixed powders of dry fumedsilica and 5 wt % of carbon black sealed in a gas-permeable non-wovenfabric bag. In enveloping member 3, polychlorotrifluoroethylene (50μm-thick) having a melting point of 210° C. is used for heat seal layer5, aluminum foil (6 μm-thick) is used for gas barrier layer 6,polyethylenenaphthalate (12 μm-thick) having a melting point of 270° C.is used for a first protective layer 7, and tetrafluoroethylene-ethylenecopolymer (25 μm-thick) having a melting point of 260° C. is used forsecond protective layer 8. In sample 5, as radiation heat transfersuppressor 4, a cupper foil is used. In sample 6, an aluminum foil isused. In sample 7, a nickel foil is used.

Similar to the first exemplary embodiment, the results of evaluatingheat-insulating performance are shown in Table 2.

TABLE 2 Sample Metal Surface temperature on No. foil low-temperatureside 5 Copper foil 45° C. 6 Aluminum foil 40° C. 7 Nickel foil 42° C.Body 1A None 80° C.

As obvious from Table 2, in samples 5 to 7, heat-insulating performanceis larger than that of the case structured like sample 5 without nometal foil placed on vacuum heat insulator body 1A (body 1A).

In sample 6, the temperature is 5° C. lower than that of sample 5. Insample 7, the temperature is 3° C. lower and the heat-insulatingperformance is larger than those of sample 5. This is because theinfrared reflectance of an aluminum foil is 0.75 and the infraredreflectance of a nickel foil is 0.65, which are more excellent than thatof a cupper foil, i.e. 0.55. Additionally, having more excellentcorrosion resistance than those of aluminum and cupper the nickel foilexhibits stable effects of suppressing radiation heat transfer for anextended period of time.

Next, a film having metal deposition on a resin substrate is placed asradiation heat transfer suppressor 4. The results obtained by changingthe kinds resin substrate and deposited metal are shown in samples 8 to11. Core 2 and enveloping member 3 are the same as those of sample 5. Insample 8, as a metal deposition film, polyethyleneterephthalate (PET)film is used for a resin substrate and aluminum is deposited thereon. Insample 9, as a metal deposition film, polyphenylene sulfide (PPS) filmis used for a resin substrate and aluminum is deposited thereon. Insample 10, as a metal deposition film, tetrafluoroethylene-ethylenecopolymer (PTFE-PE) film is used for a resin substrate and aluminum isdeposited thereon. In sample 11, as a metal deposition film, PTFE-PEfilm is used for a resin substrate and nickel is deposited thereon.

Similar to the first exemplary embodiment, the results of evaluatingheat-insulating performance are shown in Table 3.

TABLE 3 Surface temperature on Sample No. Deposited Metal Resinsubstrate low-temperature side 8 Aluminum PET 44° C. 9 Aluminum PPS 44°C. 10 Aluminum PTFE-PE 42° C. 11 Nickel PTFE-PE 44° C. Body 1A None None80° C.

As obvious from Table 3, in samples 8 to 11, heat-insulating performanceis larger than that of the case structured like sample 8 without anymetal deposition film placed on vacuum heat insulator body 1A. Becausethe melting points of the resin substrates are 200° C. or higher, theresin substrates do not melt out even in a high-temperature atmosphereof approx. 150° C. This advantage can exert excellent effect ofsuppressing heat radiation and provide excellent heat-insulatingperformance.

Metals, such as aluminum, nickel, cupper, gold, and silver, can bedeposited. In the view point of improving heat-insulating effects, it ispreferable that the infrared reflectance in a wavelength ranging from 2μm to 25 μm is 20% or higher. Desirably, it is 50% or higher. Any resinsubstrate at temperatures and under conditions in the metal depositionprocess can be used, without special limitation. PET film, PPS film, andvarious kinds of fluorocarbon films can be used.

Methods of heating metals to an atomic state suitable for deposition areused for deposition under a reduced pressure or normal pressure. Theheating methods are not specified; however, high-frequency waveapplication, electron beam, laser, or other methods can be used.

Generally, metal deposition films have high reflectance of infraredrays, higher flexibility than metal foils, and higher handling property.For these reasons, metal deposition films have high productivity, exerthigher effects of suppressing radiation heat, and provide a vacuum heatinsulator having excellent heat-insulating performance.

In sample 8, because the radiation heat suppressor exceeds a temperatureof 105° C., which is the relative temperature index value (UL746B) ofthe PET film, under conditions of radiation at 150° C., the radiatedsurface is slightly shrunken by softening. In contrast, the radiatedsurface is not shrunken by softening even in radiation at 150° C. insample 9, and appearance is improved. This is because the melting pointof the PPS film is 285° C., and the relative temperature index value (UL746B) is 160° C., and thus the sample has an excellent heat-resistingfunction. Having a melting point of 285° C. and extremely excellentheat-resisting function, the PPS film is not softened or shrunken evenunder conditions at temperatures around 150° C. For this reason, the PPSfilm exerts excellent effects of suppressing radiation heat for anextended period of time and provides a vacuum heat insulator havingexcellent heat-resisting performance. Additionally, as a generalengineering plastic resin substrate, the PPS film is often used formetal deposition, relatively inexpensive, and excellent in appearance.

For sample 10, the surface temperature on the low-temperature side is42° C., which is 2° C. lower than that of sample 8. In sample 10, aPTFE-PE film having a relatively small range of absorption wavelengthsin an infrared ray area is used as a resin component. It is consideredthat this film suppresses an increase in solid heat conduction caused byabsorption of heat rays in resin components contained in the substrate.

In radiation at 150° C., the radiated surface is not shrunken bysoftening and the appearance is improved. This is because the PTFE-PEfilm has a melting point of 260° C. and the relative temperature indexvalue of 150° C. (UL 746B), and thus has an excellent heat-resistingfunction. Having corrosion and chemical resistance together with heatresistance, the fluorocarbon resin film exerts excellent effects ofsuppressing heat radiation for an extended period of time and providesexcellent heat-insulating performance even under sever conditions ofuse, such as high humidity.

For sample 11, the surface temperature on the low-temperature side is44° C. and the performance similar to that of sample 8 is provided. Thesample 11 has higher corrosion resistance than that of aluminumdeposition and exhibits stable effects of suppressing radiation heattransfer for an extended period of time.

FOURTH EXEMPLARY EMBODIMENT

Next, a description is provided of the effect of a core, using a vacuumheat insulator with a coating of radiation heat transfer suppressor 4,as an example.

First, a vacuum heat insulator with a coating is described. The basicstructure of the coating is similar to that of sample 2 in accordancewith the first exemplary embodiment. Core 2 and enveloping member 3 arealso the same as those in the first embodiment.

Materials capable of holding a space as core 2 of vacuum heat insulator1, such as fiber materials, e.g. glass wool and rock wool, powdermaterials, e.g. wet silica, dry silica and zeolite, and open-cell foamscan be used as core 2. In consideration of use at high temperatures,powder materials having minute voids are suitable.

For sample 12, dry humed silica sealed into an air-permeable non-wovenfabric bag is used as core 2. For sample 13, a uniformly mixed powder ofdry humed silica and 5 wt % of carbon black added thereto is prepared,and sealed into an air-permeable non-woven bag. Used for sample 14 is amolded mixture of powders and fabric material, i.e. dry humed silica, 5wt % of carbon black, and 10 wt % of glass wool.

Similar to the first exemplary embodiment, the results of evaluatingheat-insulating performance of vacuum heat insulation 1 are shown inTable 4.

TABLE 4 Surface temperature on Sample No. Core low-temperature side 12Dry humed silica 58° C. 13 Dry humed silica + 48° C. carbon black 14 Dryhumed silica + carbon black + glass wool 60° C. Body 1A Dry humed silica80° C. 2 Glass wool 58° C.

Body 1A in Table 4 is a vacuum heat insulator having dry humed silica ascore 2, and no coating formed thereon. As obvious from Table 4, in everysample other than body lA, the surface temperature on thelow-temperature side is lower than that of body 1A. This is becauseleafing aluminum flake pigment reflects infrared rays and thussuppresses absorption of the heat of infrared rays. Sample 12 hasperformance similar to sample 2 which has the same structure except forglass wool as core 2.

For sample 13, the surface temperature on the low-temperature side is10° C. lower than that of sample 12. This considerably improvesheat-insulating performance. Carbon black, an electrically conductivepowder, is considered to disaggregate agglomerated particles of humedsilica to reduce the void diameter of core 2. As a result, effects ofdecreasing gas heat conductivity and effects of reducing solid heatconductivity caused by reduction in contact areas of fined individualparticles provide excellent heat-insulating effects. For this reason,this material is particularly preferable to be used underhigh-temperature conditions of large movement of air molecules.

Dry silica is specified because it has excellent effects in whichelectrically conductive powders disaggregate agglomerated particles, andexert more excellent heat-insulating effects by pulverization. Forsample 13, the degree in which temperature increase reduces theheat-insulating performance and the degree in which an increase in theinternal pressure of the vacuum heat insulator reduces theheat-insulating performance are higher than those in use of general corematerials, such as glass wool. Because the disaggregated agglomeratedparticles form the void diameters in the inner layers, the voiddiameters are extremely small. As a result, it is considered that anincrease in kinetic momentum of air molecules caused by increases intemperature and pressure is suppressed, and deterioration of gas heatconductivity is prevented. These advantages provide heat-insulatingperformance around 150° C. and improve reliability with time.

As dry silica used for core 2, silicon oxide compounds having a variouskinds of grain diameters produced by dry process, e.g. silicate by thearc process, and silicate by thermal decomposition, can be used. Suchdry silica has relatively weak electrostatic force between agglomeratedparticles and large effects of disaggregating agglomerated particleswhen electrically conductive powders are added. Because of its excellentheat-insulating performance, those having a primary grain diameter up to50 nm are preferable. Especially when a high heat-insulating performanceis necessary, those having a primary grain diameter up to 10 nm aredesirable.

Dry silica having various kinds of grain sizes can also be used. Forexample, products out of the normal lots of which grain sizes are notcontrolled between those of product A and product B both having thespecified grain sizes can be used. Generally, these products can beobtained at a lower cost.

Any powder having electrical conductivity can be used as electricallyconductive powders of core 2. As a general measure, powders having apowder specific resistance, i.e. a measure of conductivity, up to1×10¹³Ω/cm are preferable. Preferable materials in inorganic powdersinclude metal oxide powders, carbonate powders, chloride powders, andcarbon powders. Preferable materials in organic powders includemetal-doped powders. It is more preferable that the powder specificresistance is up to 1 ×10⁸Ω/cm. When higher heat-insulating performanceis required, it is preferable that the powder specific resistance is upto 10 Ω/cm. When carbon powders are used as a conductive powder, itspowder specific resistance is small and ranges from 0.1 Ω/cm to 5 Ω/cm.The carbon powders have excellent effects of disaggregating agglomeratedparticles of dry silica and improving heat-insulating performance. Thecarbon powders are extremely useful, because of its industrial low cost.

In consideration of a uniform mixture of the powder with the basematerial, it is preferable that the diameters of the particles aresmaller. Further, it is desirable that the content of conductive powdersis up to 60 wt %. When the content exceeds 60 wt %, the solid heatconduction of the conductive powder has a larger influence and maydegrade the performance of the heat-insulating member. The appropriateamount of addition varies with the kinds of powders to be added. Evenwith addition of 60% or more, the effect reaches saturation in manycases. Thus, the appropriate content of the conductive powders is up to60 wt %. More desirably, it is up to 45 wt %.

In sample 14, the surface temperature on the low-temperature side is 60°C. However, because core 2 is molded, the sample has higher handlingproperty than sample 12. In other words, because glass wool works as anaggregate, a heat-insulating molded body can easily be formed by generalcompression molding. Additionally, filling powders into a non-woven bagis unnecessary and thus material costs and production costs can bereduced. Because the core is molded, it does not generate powdery dust.This advantage prevents the adhesion of powders to the sealing openingand inhibition of sealing property when the core is inserted intoenveloping member 3 and sealed under a reduced pressure. This advantagealso prevents gradual entry of air into the heat insulator (slow leak).Thus, the reliability of vacuum heat insulator 1 can be ensured for anextended period of time.

Incidentally, moisture absorbent or gas absorbent can be sealed togetherwith core 2 to absorb little gas. Moisture absorbents and gas absorbentsinclude physical absorbents such as synthetic zeolite, activated carbon,active alumina, silica gel, dowsonite and hydrotalcite, and chemicalabsorbents such as the oxides and hydroxides of alkali metals and alkaliearth metals. Because such a gas may be generated from core 2 for anextended period of time or enter through enveloping member 3, it cannotbe prevented. However, using such absorbents allows the reliability tobe ensured for an extended period of time.

In order for vacuum heat insulator 1 to exhibit excellentheat-insulating property, the appropriate average density of vacuum heatinsulator 1 ranges from 100 kg/m³ to 240 kg/m³. At a density smallerthan 100 kg/m³, it is difficult to be held as a mold. At a densitylarger than 240 kg/m³, overall high density increases solid heatconductivity and decreases heat-insulating property.

In sample 14, glass wool is mixed with core 2. Inorganic fibers otherthan glass wool can be used. Such inorganic fibers include aluminafiber, silica alumina fiber, silica fiber and the like as ceramicfibers. As glass fibers, fibrous glass, zirconia fiber, rock wool,calcium sulfate fiber, silicon carbide fiber, potassium titanate fiber,magnesium sulfate fiber, or other known material can be used withoutlimitation. Preferable materials are alumina fiber, silica aluminafiber, silica fiber, glass wool, fibrous glass and the like, which haveexcellent affinity with silica having a hydroxyl group on its surface,because they have larger effects as an aggregate. Desirably, thesurfaces of these fibers are not treated with phenol or the like.

A description is provided of a variation with long time of heatconductivity and flame retardance given by the effect of envelopingmember 3 in the present embodiment. Similar to the first exemplaryembodiment, every film in enveloping member 3 has flame retardance.

Heat conductivity of vacuum heat insulator 1 using these materials ismeasured to 0.004 W/mK. The heat conductivity after an acceleration testin which vacuum heat insulator 1 is left in an atmosphere at 150° C. forfive years is measured to 0.010 W/mK. Even after five years, excellentheat-insulating property is maintained.

When flammability of the vacuum heat insulator is confirmed according toTest for Flammability of Plastic Materials for Parts in Devices andAppliance specified in UL94 safety standard, results equivalent to V-0of this standard are obtained.

Because a material having a melting point of 200° C. or higher isselected, welded heat seal layer 5 does not melt even in ahigh-temperature atmosphere of 150° C. This selection of material caninhibit a decrease in gas-barrier property of heat seal layer 5 anddeterioration of heat conductivity, and maintain heat-insulatingperformance of the vacuum heat-insulator for an extended period of time.

The melting points of gas-barrier layer 6 and protective layers 7 and 8are higher than the melting point of heat seal layer 5. This structureprevents the materials from melting out when heat seal layer 5 iswelded, and affecting the reliability of vacuum heat insulator 1 in themanufacturing process thereof. Especially in application to the productsin high-temperature use, this structure can ensure stable quality asvacuum heat insulator 1. Further, as enveloping material 3 having alaminate structure, and as vacuum heat insulator 1, this structurerenders flame retardance and improves the safety of vacuum heatinsulator 1 during use.

The resin films used for heat seal layer 5 are not specified if they canbe heat-welded at temperatures of 200° C. or higher. Desirable resinfilms are polyethylenenaphthalate having a melting point of 270° C. anda fluorocarbon resin film such as polychlorotrifluoroethylene having amelting point of 210° C., polyethyleneterephthalate having a meltingpoint of 260° C., fluorocarbon resin films such astetrafluoroethylene-ethylene copolymer having a melting point of 260°C., and tetrafluoroethylene-hexafluoropolypropylene copolymer having amelting point of 285° C. The polychlorotrifluoroethylene film is easy touse because of its low melting point among fluorocarbon films, andeconomical.

For gas-barrier layer 6, films having a melting point higher than thatused in heat seal layer 5 and having metal foil, deposited metal ordeposited inorganic oxide thereon can be used without any specification.A resin film having high gas-barrier property can also be used withoutany specification. For example, as a metal foil, an aluminum foil isoften used. As metals into which low calories flow along the metal foilaround the vacuum heat insulator, iron, nickel, platinum, tin, titanium,stainless and carbon steels can be used. As materials of depositedmetal, aluminum, cobalt, nickel, zinc, cupper, silver or mixturesthereof can be used. As materials of deposited inorganic oxide, silicaand alumina can be used. As resin films for the substrate of deposition,polyethylenenaphthalate and polyimide film can be used.

For protective layers 7 and 8, any film having a melting point higherthan those of the films used for heat seal layer 5 can be used.Specifically, when a tetrafluoroethylene-ethylene copolymer having amelting point of 260° C. is used for heat seal layer 5, the materialsusable for the protective layer include:tetrafluoroethylene-perfluoroalkoxyethylene copolymer having a meltingpoint of 310° C.; tetrafluoroethylene having a melting point of 330° C.;and polyether-ketone having a melting point of 330° C. Polysulfone andpolyether-imide can also be used.

In the above description, a vacuum heat insulator having a coatingprovided as radiation heat transfer suppressor 4 is used as an example.However, the structure of radiation heat transfer suppressor 4 is notlimited to the above. Laminated inorganic materials in the secondembodiment and metal films in the third embodiment can also be used asradiation heat transfer suppressor 4 with the similar effects.

Hereinafter, a description is provided of relations between the heatgeneration source and radiation heat transfer suppressor 4 in the firstto fourth exemplary embodiments.

In the case where radiation heat transfer suppressor 4 for suppressingabsorption of infrared rays in the outermost layer of vacuum heatinsulator body 1A is provided, effects can be obtained only when theinfrared rays reach the outermost layer. For this reason, in order toinhibit radiation heat transfer caused by infrared rays, it is importantto dispose vacuum heat insulator 1 so that absorption of the infraredrays in the outermost layer can be inhibited.

Generally, radiation heat transfer is caused by absorption of infraredrays having wavelengths mainly ranging from 2 to 25 μm by a solid. Thus,it is important that the outermost layer of the sold has functions ofsuppressing the infrared rays and far infrared rays. However, when theheat generation source is in direct contact with radiation heat transfersuppressor 4, the heat energy conducts inside of the solid by solid heatconduction and thus the effect of suppressing radiation heat cannot beexerted.

For this reason, it is preferable that space 16 for passing infraredrays is provided between heat generation source 15 and radiation heattransfer suppressor 4 as shown in FIG. 7. In other words, vacuum heatinsulator body 1A is placed between object-to-be protected 17 and heatgeneration source 16; radiation heat transfer suppressor 4 is placedbetween body 1A and heat generation source 16. With this structure, theinfrared rays from the heat generation source directly reaches radiationheat transfer suppressor 4 without being inhibited by another solid. Asa result, heat energy does not make solid heat conduction from the othersolid to radiation heat transfer suppressor 4, and radiation heattransfer suppressor 4 directly receives the infrared rays and does notabsorb it as heat but reflects it. For this reason, the functions ofinhibiting solid heat conduction and radiation heat transfer made tovacuum heat insulator body 1A provide excellent heat-insulatingperformance.

The location of radiation heat transfer suppressor 4 is not specificallylimited, and it may be disposed between the surface of enveloping member3 and heat generation source 16. As shown in FIG. 8, the radiation heattransfer suppressor can be disposed out of contact with the surface ofthe enveloping member. As shown in FIG. 9, the radiation heat transfersuppressor can be disposed in partial contact with the surface of theenveloping member.

To dispose the radiation heat transfer suppressor in partial contactwith the surface of the enveloping member as shown in FIG. 9,irregularities can be provided on radiation heat transfer suppressor 4.Additionally, any bonding measures for adhesion, such as various kindsof organic or inorganic adhesives, hot melt, and double-faced tape, canbe used.

Space 16 is effective if only a small space in which infrared wavespropagate is maintained. The space can be set as required according tothe relation between the temperature of heat generation source 15 andheat resistance of enveloping member 3. Space 16 is not only an airlayer but can be various kinds of gases, such as argon, nitrogen, andcarbon dioxide, or a vacuum.

Heat generation source 15 is not only a heater powered by electricity,gas, or the like, but any heat generation source responsible for thetemperature gradient of the surface on the high-temperature side withrespect to the surface on the low-temperature side of installed vacuumheat insulator 1. For example, in some applications of vacuum heatinsulator 1, outdoor temperatures are included in heat generation source15.

FIFTH EXEMPLARY EMBODIMENT

A description is provided of an electric kettle, as an example of a heatinsulator in which the surface having radiation heat transfer suppressor4 is faced to a heat generation source side.

FIG. 10 is a sectional view of an electric kettle in accordance with thepresent embodiment. Electric kettle 22 has hot-water storage (hereinafter referred to as “storage”) 23 for boiling water and storing hotwater, and openable/closable lid 24 for covering the top surfacethereof. Donut-shaped heater 25 is attached to the bottom surface ofhot-water storage 23 in intimate contact therewith. Temperature sensor27 senses the temperature of water. Control unit 26 receives signalsfrom temperature sensor 27 to control heater 25 so that the temperatureof the hot water can be maintained at a predetermined temperature.Hot-water pipe 32 communicates from water inlet 28, provided on thebottom, to water outlet 31. Depressing press button 33 activates pump 30driven by motor 29 so that hot water comes out from the electric kettle.

On the side face of storage 23, vacuum heat insulator 1 having radiationheat transfer suppressor 4 on the side of storage 23 is wrapped. Alsooutside of heater 25 on the bottom face of storage 23, vacuum heatinsulator 1 having radiation heat transfer suppressor 4 faced to theside of heater 25 is disposed. This structure inhibits escape of theheat of storage 23 and a decrease in the temperature of hot water.Vacuum heat insulator 1 has a structure shown in any one of the first tofourth embodiments.

In this structure, vacuum heat insulator 1 is disposed on the bottomface in which a conventional insulating material cannot be disposedbecause of the high temperature to insulate the heat. Vacuum heatinsulator 1 effectively reflects infrared rays radiated from the heatradiation source, so that the power consumption is reduced by approx.5%. The performance is maintained for a long period of time. Inaddition, on the bottom surface of the body, a space need not beprovided for heat insulation. This reduces the volume below storage 23,thus making electric kettle 22 compact.

When vacuum heat insulator 1 is used as a heat-insulating member, it canbe used for hot/cold insulation equipment requiring heat or keep warm inan operating temperature ranging from −30° C. to 150° C. It is usefulfor applications in equipment for generating heat in the same operatingtemperature range, such as a rice cooker, dish washer, electric kettle,automatic vendor, toaster, breadmaker, and induction heating (IH) stove.The vacuum heat insulator is also useful in a thin space, and foreffective use by reduction of heat-insulating space. Further, it is alsouseful for not only electric equipment but also gas equipment, such as agas stove.

SIXTH EXEMPLARY EMBODIMENT

A description is provided of a notebook type computer, as an example ofusing a heat-blocking member in which the surface having radiation heattransfer suppressor 4 of heat insulator 1 of the present invention isfaced to the high-temperature side.

FIG. 11 is a sectional view of a notebook type computer in accordancewith the present embodiment. Notebook type computer (herein afterreferred to as “computer”) 35 incorporates printed circuit board 36having CPU 37 and other chips mounted thereon. Cooling unit 38 isprovided to stabilize the performance of CPU 37, which reaches aconsiderably high temperature during operation. Cooling unit 38 has heattransfer block 39 in contact with CPU 37 and heat pipe 40 for heattransfer. Radiator plate 41 diffuses the inside heat and transfers it tobottom surface 43 of computer 35 to radiate the heat. Vacuum heatinsulator 1 has any one of the above-mentioned structures of the firstto fourth embodiments. Vacuum heat insulators 1 are attached to theinside of bottom surface 43 directly below CPU 37, and to the rearsurface of keyboard 44 directly above CPU 37 with their radiation heattransfer suppressors 4 faced to the high temperature side by an adhesivein a manner to make intimate contact therewith.

This installation of vacuum heat insulators can decrease thetemperatures by 8° C. at the maximum on bottom surface 43 and inhigh-temperature portions on the surface of keyboard 44 directly aboveCPU 37. In other words, radiation heat transfer suppressor 4 effectivelyreflects the infrared rays generated from the heat generation portionheated by CPU 37, such as heat transfer block 39, and inhibits the heattransfer. Vacuum heat insulator 1 having excellent heat-insulatingperformance in a high-temperature insulates the heat of solid heatconduction portion. Thus, abnormally heating a part of the surface ofcomputer 35 and an uncomfortable feeling to the users can be prevented.

Additionally, because extremely thin radiation heat transfer suppressor4 is provided on the surface of vacuum heat insulator 1 having a 2mm-thick molded core, the vacuum heat insulator is suitable forapplications in which the volume for heat insulation is limited, such ascomputer 35.

If enveloping member 3 is structured of the above-mentionedflame-retardant and heat-resistant materials, it is applicable tocomputer 35. This structure can prevent an uncomfortable feeling that isgenerated by a part of the surface of computer 35 abnormally heated fora long period of time while the safety of computer 35 is improved.

Vacuum heat insulator 1 can be used to heat-insulate and protect a harddisk drive and the like built in computer 35 from high temperatures.Vacuum heat insulator 1 is also applicable to products that requirereduction in size and thickness in the limited space in which aheat-insulating member is used. For example, the heat insulator can beused for heat-insulation between the liquid crystal part in a carnavigation system having a liquid crystal panel, and the part in which aCPU generates heat, and heat-insulation of the controller of afluorescent lamp incorporating an inverter.

SEVENTH EXEMPLARY EMBODIMENT

A description is provided of a projector, as an example of using aheat-blocking member in which the surface having radiation heat transfersuppressor 4 of heat insulator 1 of the present invention is faced tothe high-temperature side.

FIG. 12 is a sectional view of a projector in accordance with thepresent embodiment. Projector 45 of a digital light processing (DLP)system is composed of lamp 46, digital micromirror device (DMD) element47, color filter 48, ballast 49, power source board 50, control board51, cooling fan 52, lens 53, and housing 54. The light emitted from lamp46 is reflected onto color filter 48 and reaches DMD element 47 toproject an image through lens 53.

Vacuum heat insulator 1 described in the first to fourth exemplaryembodiments is disposed between lamp 46 and housing 54. This structureprevents the temperature increase of housing 54 even when the surfacetemperature of lamp 46 reaches 180° C. Vacuum heat insulators 1 are alsodisposed between color filer 48 and control board 51, and power sourceboard 50 and control board 51. Vacuum heat insulator 1 reflects infraredrays generated from lamp 46 and power source board 50 and protectselectronic circuit boards susceptible to heat. At that time, radiationheat transfer suppressor 4 is faced to lamp 46 and power source board50, i.e. heat generation sources.

In the present embodiment, a DLP projector of 1-chip projection systemis described. The same effects can be obtained in the 2-chip projectionsystem and 3-chip projection system. The description is provided of aprojector of the DLP system. The same effects can be obtained in aprojector of a liquid crystal system.

EIGHTH EXEMPLARY EMBODIMENT

A description is provided of a printing machine, as an example of usinga heat-blocking member in which the surface having the radiation heattransfer suppressor of the heat insulator of the present invention isfaced to the high-temperature side.

FIG. 13 is a schematic sectional view of a printing machine inaccordance with the present embodiment. Printing machine 64 includingfixing unit 63 prints images onto recording paper 65. At this time, astatic electric charge image is formed on the surface of photoconductordrum 66, and toner is adsorbed onto the image from toner storage 67.Then, the toner is transferred onto recording paper 65 via transfer drum68. Recording paper 65 having the toner image transferred thereon isdelivered into fixing unit 63, where recording paper 65 passes betweenheat-fixing roller 69 and press-contacting roller 70 both kept at hightemperatures so that the toner is melted and fixed on the recordingpaper.

Around heat-fixing roller 69 and press-contacting roller 70, vacuum heatinsulator 1 shown in the first to fourth exemplary embodiments isdisposed in proximity thereto in order to maintain predetermined hightemperatures. At this time, vacuum heat insulator 1 is formed into acylindrical shape having a slit, and disposed so that radiation heattransfer suppressor 4 is on the high-temperature side. Placement of thevacuum heat insulator improves printing quality, reduces the time forstart and restart, and power consumption.

Additionally, vacuum heat insulator 1 for blocking heat is disposed onthe entire side walls and top surface of an outer frame of fixing unit63 with radiation heat transfer suppressor 4 faced to thehigh-temperature side to prevent thermal effect on its environment.Vacuum heat insulators 1 can further be disposed to block the heatbetween fixing unit 63 and any one of toner storage 67, photoconductivedrum 66 and transfer drum 68. Placement of vacuum heat insulatorsimproves printing quality and keeps a controller (not shown) and atransfer unit including toner storage 67 and photosensitive drum 66, totemperatures up to 45° C., at which adverse effects are not given totoner, for a long period of time.

The vacuum heat insulator of the present invention can be used in theproducts in which a heat generation source up to 150° C. is need to beheat-insulated or kept warm other than the fixing units of a copyingmachine and laser printer, i.e. printing machines.

As described above, in equipment of the fifth to eighth exemplaryembodiments, vacuum heat insulator 1 is used as a heat-blocking memberwith the surface of the vacuum heat insulator having radiation heattransfer suppressor 4 faced to the high-temperature side. Such placementcan maintain heat-insulating performance during use for an extendedperiod of time under relatively high-temperature conditions around 150°C., and provide excellent heat-insulating performance.

In the fifth to eighth exemplary embodiments, as described in the latterpart of the fourth exemplary embodiment, it is preferable to provide aclearance between the heat generation source and radiation heat transfersuppressor 4. It is also preferable to produce vacuum heat insulatorbody 1A and radiation heat transfer suppressor 4 separately, and provideradiation heat transfer suppressor 4 between vacuum heat insulator body1A and the heat generation source.

INDUSTRIAL APPLICABILITY

The vacuum heat insulator of the present invention has an excellentheat-insulating performance at relatively high temperatures around 150°C., and can be used while maintaining heat-insulating performance for anextended period of time. For this reason, providing the vacuum heatinsulator in the important parts of various kinds of installations andoffice equipment, which need heat insulation or keep warm, contributesto energy saving, protection of components susceptible to heat,downsizing and improvement of the unit.

1. A vacuum heat insulator comprising: a core; a gas-barrier envelopingmember covering the core and having a depressurized inside; and aradiation heat transfer suppressor provided on at least one surfaceamong external surfaces of the enveloping member, wherein the radiationheat transfer suppressor has a first inorganic material film, and asecond inorganic material film having a reflectance different from thatof the first inorganic material film, and the first inorganic materialfilm and the second inorganic material film are alternately laminatedwith each other.
 2. The vacuum heat insulator according to claim 1,wherein the first inorganic material film and the second inorganicmaterial film are alternately laminated in a thickness of a quarter of awavelength providing maximum emissivity at a heat-insulatingtemperature.
 3. The vacuum heat insulator according to claim 1, whereincombination of the first inorganic material film and the secondinorganic material film is any two selected from magnesium fluoride,calcium fluoride, lithium fluoride, barium fluoride, thalliumbromo-iodide, thallium bromo-chloride, sodium chloride, potassiumbromide, potassium chloride, silicon oxide, cesium iodide, and zincselenide.
 4. A vacuum heat insulator comprising: a core; a gas-barrierenveloping member covering the core and having a depressurized inside;and a radiation heat transfer suppressor provided on at least onesurface among external surfaces of the enveloping member, wherein theradiation heat transfer suppressor includes a resin substrate and ametal film provided on the resin substrate, the resin substrate is aresin film having a melting point of at least 200 degrees C., and theresin film is a polyphenylene-sulfide film.
 5. An apparatus comprising:a vacuum heat insulator having: a core; and a gas-barrier envelopingmember covering the core and having a depressurized inside; a heatgeneration source; and a radiation heat transfer suppressor providedbetween the vacuum heat insulator and the heat generation source;wherein the radiation heat transfer suppressor has a first inorganicmaterial film, and a second inorganic material film having a reflectancedifferent from that of the first inorganic material film, and the firstinorganic material film and the second inorganic material film arealternately laminated with each other.
 6. The apparatus according toclaim 5, wherein a space is provided between the heat generation sourceand the radiation heat transfer suppressor.
 7. The apparatus accordingto claim 5, wherein the radiation heat transfer suppressor is formed onat least one surface among external surfaces of the enveloping member.8. An apparatus comprising: a vacuum heat insulator having: a core; anda gas-barrier enveloping member covering the core and having adepressurized inside; a heat generation source; and a radiation heattransfer suppressor provided on at least one surface among externalsurfaces of the enveloping member, wherein the radiation heat transfersuppressor includes a resin substrate and a metal film provided on theresin substrate, the resin substrate is a resin film having a meltingpoint of at least 200 degrees C., and the resin film is apolyphenylene-sulfide film.